1. Field of the Invention
This invention is directed to the manufacture of unique high modulus composite wheel structures having a fiber reinforced syntactic foam core and disc member; these structures can be fabricated, for example, to produce automotive wheels for pneumatic tires which are lightweight and have compressive strength and modulus.
2. Description of the Prior Art
The design concepts and production techniques used in the manufacture of vehicle wheels for the automotive industry have not been significantly changed for many years. The only notable exception was the introduction of styled wheels in the 1960's. Styled wheels do not require hubcaps or other wheel covers, and their popularity has grown continuously since their introduction. Nonetheless, the conventional steel disc wheel still predominates in the automotive industry.
Vehicle wheels have been fabricated from synthetic plastic materials as illustrated in U.S. Pat. No. 3,790,220. As noted in this patent, these wheels have not been competitive with steel wheels. Rather plastic wheels have been especially, though not exclusively, intended for use with vehicles such as transport carts, fork lifts, and the like, having small diameter wheels.
Plastic materials are also known for use as elements in otherwise metal wheels. For example, U.S. Pat. No. 3,790,219 discloses the use of expanded polyurethane or polystyrene foam, or other honeycomb plastic material, for use as a spacer, or packing element, in wrought metal wheels; this foam lacks compressive strength and has low heat resistance. The wheels which are the subject of U.S. Pat. No. 3,790,219 are wheels manufactured from lightweight alloys such as alloys of magnesium for high performance cars.
Polyurethane foam is also known for use as an adhesive to bond ornamental plastic wheel covers to conventional steel disc wheels. U.S. Pat. No. 3,669,501 shows such an application of polyurethane foam. As pointed out in that patent, the wheel is of conventional construction, i.e., the wheel is the conventional steel disc wheel which predominates the vehicle wheel market. The polyurethane is strictly an adhesive material to secure the cover permanently to the wheel.
The vehicle wheel of U.S. Pat. No. 3,968,996 uses an organic resin foam, such as polyurethane foam, as a structural load bearing member. An inner wheel disc, an outer decorative disc, and a rim interlocked with both those discs are interconnected and bonded by polyurethane foam. The polyurethane foam serves as a load bearing and load transmitting structural member. According to one method for manufacturing the instant wheel, the wheel rim, inner wheel disc, and outer decorative disc are positioned in a die, and a polyurethane composition is then injected into the volume defined by those wheel components for curing in situ. Alternatively, a polyurethane foam preform is adhesively bonded to the rim, inner wheel disc, and outer decorative disc in an assembly die. This vehicle wheel provides style flexibility and styling attractiveness. Furthermore, the instant wheel affords improved dimensional control, improved concentricity, and improved wheel balance in a vehicle wheel further characterized by low cost and lightweight. Finally, since the resultant wheel is a solid wheel, noise control is insured.
According to U.S. Pat. No. 4,000,926, a vehicle wheel can include a structural member defining the outboard side of a wheel disc and having radial openings spaced circumferentially from each other. Ribs that are preformed are inserted through the openings projecting in an outboard direction to give the wheel a styled appearance. The ribs cooperate with the outboard structural member defining the openings and other structural members of the wheel to define an enclosed cavity that receives organic resin foam. The foam is adhered to the structural members and to the ribs to cooperate therewith as a load bearing component of the wheel.
The ribs are preferably formed by a stamping operation. The stamping tools for the ribs only have to form a single rib during each stroke. The tooling expense necessary to form the ribs is thus minimized since the tools do not have to incorporate portions for simultaneously forming each rib of the wheel. Also, this rib stamping process may proceed at a much more rapid rate than when the ribs are formed integrally with a structural member that defines the rest of the outboard extremity of the wheel. In fact, the individual rib stamping may proceed so rapidly that the number of ribs necessary, usually five, may be stamped by the required number of strokes in a shorter time than is necessary to stamp a single wheel structural member having the integral ribs. This latter stamping must be formed at a slower rate due to its larger size.
The stamped ribs preferably include flanges that engage the interior side of the outboard structural member defining the radial openings through which the ribs project. These flanges may be adhesively secured to the outboard structural member prior to receiving the foam which is preferably injected into the cavity for curing.
Conventional automotive wheels include an annular rim that supports an associated tire. A disc of the wheel is secured to the rim within its annular configuration. The central portion of the wheel disc includes holes for receiving bolts which detachably secure the wheel to an associated hub. The wheel rim and disc are conventionally made by forging of the steel stock that is of a relatively heavy gauge, i.e., on the order of one-eighth inch thickness. The outer periphery of the disc is fixedly secured to the rim by welding so that the rim and disc are inseparable. The point of separation between the components of the automotive wheel assembly thus occurs at the wheel disc and hub during replacement or repair of the associated vehicle tire. This necessarily means that each automotive vehicle having four wheel assemblies being utilized and one spare tire requires five wheels having a rim and disc. The forging process of the relatively heavy steel stock from which the wheel components are made must be carried out with sufficient accuracy so that no unbalanced forces are present during the rotation of the wheel. The heavy stock from which the wheel is forged makes this balancing somewhat more difficult than would be the case if lighter stock were utilized. However, to provide the required structural strength, such heavy stock is necessary with conventional automotive wheels.
Vehicle wheel assemblies of the more heavy duty type for use on trucks or trailers have a somewhat different construction than automotive wheel assemblies. These heavy duty wheel assembly constructions conventionally include a wheel hub that is cast or forged from steel. The disc portion of the wheel may be integral with the hub and support the brake drum or brake disc of the wheel assembly. The outer periphery of the integral hub and wheel disc detachably supports one or more wheel rims for carrying one or more tires. The heavy duty wheel assembly construction may also take another form wherein the rim and disc portions of the wheel are welded to each other and detachably secured to the wheel hub. In this construction, the brake drum or brake disc is fixedly secured to the hub. Both of these heavy duty wheel assembly constructions require a relative large amount of machining to provide the balanced wheel assembly necessary.
U.S. Pat. No. 3,874,055 discloses a method of making a vehicle wheel that is particularly designed for use as a heavy duty truck or trailer type wheel. The disc portion of this wheel is manufactured from a continuous metallic strip that is stamped to define retaining flanges. The stamped strip is then coiled into a single closed loop that is stamped radially to define spoke-like components. The central portion defined by these spoke-like components is secured to a cast for forged hub. The periphery of this stamped structure is detachably secured to a pair of rims to complete the assembly. The hub and rims of this wheel assembly are both forged or cast and may require machining to provide the necessary balance.
U.S. Pat. No. 4,035,028 is directed to vehicle wheel assemblies and components thereof that are manufactured with a foam construction so as to have light weight, good balance without any machining, and a low manufacturing cost. The foam construction includes structural members of a relatively lightweight material that are secured to each other to define an enclosed cavity that receives an organic resin foam, such as polyurethane foam. The foam may be injected into the cavity so as to adhere to the structural members during its curing. Alternately, the foam may be preformed and received between the structural members as these members are secured to each other. In the latter case, an adhesive adheres the foam to the structural members defining the cavity.
According to U.S. Pat. No. 4,107,134, the generic term "syntactic foam" is known to be directed to a variety of polymeric materials that have been lightened by inclusion of hollow spheres.
The hollow spheres which are included in the syntactic foams of this patent may be either inorganic or organic. By way of example, there can be mentioned the microballons of borosilicate glass, silica, carbon, or thermoplastic or thermoset resins, whose diameter is generally from 10 to 500 micrometers, and the "microballoons" of glass, or thermoplastic or thermoset resins, whose diameter is in most cases from 1 to 100 micrometers.
The amount, the type and the size of the hollow spheres are determined in accordance with the properties desired for the syntactic foam. Generally, there is used from 5 to 50 parts by weight of hollow spheres per 100 parts by weight of resin. However, in order to obtain syntactic foams of high compressive strength, there is preferably used from 20 to 50 parts by weight of microspheres per 100 parts by weight of resin; preferably, the microspheres will have a relatively thick glass wall and will be of small size (for example, a diameter from 10 to 250 micrometers).
According to an advantageous feature of this patent, there can also be used hollow spheres for compressive strength in admixture with other reinforcing fillers, for example fibers such as ceramic, aramid, steel, glass fibers, or asbestos or even carbon fibers, which have the advantage of improving the reinforcement of the foam, or reducing the shrinkage of the composition during curing and of imparting thereto improved mechanical properties, particularly a higher tensile strength and a better flexural strength.
A particularly convenient composition of lightened resins comprises, from 100 parts by weight of resin, from 20 to 50 parts by weight of hollow glass microspheres having a diameter from 10 to 300 micrometers and an apparent specific gravity of 0.1 to 0.4.
U.S. Pat. No. 4,082,702 is directed to the preparation of rigid polyurethane syntactic foams containing large amounts of microballoons. The numerous prior art references discussed in this patent teaches that compositions which contain hollow beads, bubbles or microballoons have been known for many years. The concept of using these hollow beads in a composition is designed to reduce the density and also reduce the high cost of the matrix material. It was observed, however, that a reduction in density also resulted in a reduction of the structural strength of the product and it was difficult to obtain maximum strength with a minimum density. Bozzacco et al. in U.S. Pat. No. 2,806,509 described one method for improving the strength at lower densities. Bozzacco et al. coated thin walled hollow beads with a metal power and a thermosetting resin and then heated these coated beads to tackify the resin and compressed this material to provide a laminate. Although such an approach may provide useful laminates, the procedure involved several steps and does require pressure and heating to make the laminates.
U.S. Pat. No. 3,968,996 is directed to the manufacture of a vehicle wheel utilizing an organic foam, such as polyurethane foam, as a structural load bearing member. An inner wheel disc, an outer decorative disc, and a rim interlocked with both those discs are interconnected and bonded by polyurethane foam. The polyurethane foam serves as a load bearing and load transmitting structural member; according to one method for manufacturing this wheel, the wheel rim, inner wheel disc, and outer decorative disc are positioned in a die, and a polyurethane composition is then injected into the volume defined by those wheel components for curing in situ. Alternatively, a polyurethane foam preform is adhesively bonded to the rim, inner wheel disc, and outer decorative disc in an assembly die. This vehicle wheel provides style flexibility and styling attractiveness. Furthermore, this wheel affords improved dimensional control, improved concentricity, and improved wheel balance in a vehicle wheel further characterized by low cost and light weight. Finally, since the resultant wheel is a solid wheel, noise control is insured.
According to U.S. Pat. No. 4,153,657, a vehicle wheel is manufactured using an organic resin foam, such as polyurethane foam, as a structural load bearing member. An inner wheel disc, an outer decorative disc, and a rim interlocked with both those discs are interconnected and bonded by polyurethane foam. The polyurethane foam serves as a load bearing and load transmitting structural member; according to one method for manufacturing this wheel, the wheel rim, inner wheel disc, and other decorative discs are positioned in a die, and a polyurethane composition is then injected into the volume defined by those wheel components for curing in situ. Alternatively, a polyurethane foam preform is adhesively bonded to the rim, inner wheel disc, and outer decorative disc in an assembly die.
Derleth U.S. Pat. No. 3,669,501 teaches that a polyurethane resin, catalyst and hardener composition may be sprayed into a cavity defined by the structural components of a wheel and foamed in situ. The spaced wheel shells include an ornamental plastic cover 14 and a metal disc 12 which are adhesively bonded together by the foam resin.
Hobaica et al U.S. Pat. No. 3,622,437 discloses a syntactic foam material for use as a buoyancy material. The foam structure is filled with a plurality of spheres, including microspheres 14. The foam is formed from polyester, epoxy, phenolic or other exothermically hardening resin.